In a test on the AC characteristics of a semiconductor device, measurements of a propagation delay time, a setup time, a hold time, a response time and so on are made on an input signal and an output signal of the semiconductor device. Generally, in the test configuration, the power supply unit and the measuring unit of an LSI tester are respectively connected to a power supply terminal and a terminal to be tested of the semiconductor device.
A method of testing the AC characteristics of a semiconductor device will be simply described below. As an example, the following will describe a test on the AC timing characteristics of a logic LSI and so on. When the AC timing characteristics of an input signal are tested, first, a test signal is inputted to a terminal to be tested (an input terminal or an input/output terminal) and a clock signal having a given phase difference beforehand from the test signal is inputted to a clock terminal. Next, a signal latched by a first stage flip-flop connected to the terminal to be tested is compared with an expected value. After that, the delay time and the phase difference of the input signal relative to a reference signal are measured based on the comparison result. On the other hand, when the AC timing characteristics of an output signal are tested, the internal circuit of the semiconductor device is operated to transmit the output signal from a terminal to be tested (an output terminal or an input/output terminal) to the outside of the semiconductor device. After that, the delay time and the phase difference of the output signal relative to the reference signal are measured by comparing the output signal having been transmitted to the outside with the expected value at a desired time.
Moreover, in tests on the AC characteristics of semiconductor devices, a plurality of semiconductor devices have been simultaneously tested in order to suppress the cost of the tests. In other words, the power supply unit and the measuring unit of an LSI tester are respectively connected to the power supply terminal and a terminal to be tested of each semiconductor device, and power and signals are supplied to the semiconductor devices at the same timing, so that the plurality of semiconductor devices are simultaneously tested.
However, in recent years, semiconductor devices have had a larger number of pins and the number of measuring units has been more frequently deficient in simultaneous tests on a plurality of semiconductor devices. This is because in tests on AC characteristics in the prior art, the number of measuring units has to be at least as many as the total number of terminals to be tested of a plurality of semiconductor devices to be simultaneously tested.
Further, in a proposed method, a path connecting one terminal to terminals to be tested is provided in a semiconductor device, so that the AC characteristics of a large number of terminals to be tested can be tested using a small number of terminals (for example, see Japanese Patent Laid-Open No. 10-288647).
This method can suppress the number of terminals of semiconductor devices connected to the measuring units of an LSI tester. Thus it is possible to test the AC characteristics of semiconductor devices with a small number of measuring units and increase the number of semiconductor devices which can be simultaneously tested.
However, only with the path connecting one terminal to terminals to be tested in a semiconductor device, the terminals to be tested have to be tested one by one, so that the test time increases and the test efficiency does not improve.